Methods and apparatuses for encoding and decoding motion vector

ABSTRACT

Encoding and decoding a motion vector using a motion vector of a current block of a current picture, which indicates a region corresponding to the current block in a first reference picture and one of generating a motion vector predictor from a motion vector of the adjacent block having a motion vector referring to the first reference picture among adjacent blocks encoded before the current block and a motion vector of an adjacent block referring to a second reference picture other than the first reference picture.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/362,809, filed on Jul. 9, 2010, in the United States Patent andTrademark Office, and priority from Korean Patent Application No.10-2011-0019100, filed on Mar. 3, 2011, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein in byreference in their entireties.

BACKGROUND

1. Field

Exemplary embodiments relate to methods and apparatuses for encoding anddecoding a still image and a moving image, and more particularly, tomethods and apparatuses for encoding and decoding a motion vector of acurrent block by predicting the motion vector.

2. Description of the Related Art

In Codec, such as MPEG-4 H.264 or MPEG-4 advanced video coding (AVC),motion vectors of pre-encoded blocks adjacent to a current block areused to predict a motion vector of the current block. Here, a median ofmotion vectors of previously encoded blocks adjacent to left, top, andupper right of a current block is used as a motion vector predictor ofthe current block.

SUMMARY

Exemplary embodiments provide methods and apparatuses for encoding anddecoding a motion vector.

According to an aspect of the exemplary embodiments, there is provided amethod of encoding a motion vector, the method comprising: performingmotion estimation on a current block of a current picture and generatinga motion vector of the current block, the motion vector of the currentblock indicating a region in a first reference picture that correspondsto the current block, based on the motion estimated current block;determining whether an adjacent block having a motion vector referringto the first reference picture exists from among adjacent blocks encodedbefore the current block; one of generating a motion vector predictorusing the determined motion vector of the adjacent block referring tothe first reference picture, in response to determining that theadjacent block having the motion vector referring to the first referencepicture exists, and generating the motion vector predictor by using amotion vector of an adjacent block referring to a second referencepicture other than the first reference picture, in response todetermining that the adjacent block having the motion vector referringto the first reference picture does not exist; and encoding a differencebetween the motion vector predictor and the motion vector of the currentblock as motion vector information of the current block.

According to another aspect of the exemplary embodiments, there isprovided a method of decoding a motion vector, the method comprising:decoding from a bitstream motion vector predictor information thatindicates a motion vector predictor of a current block of the bitstream;decoding a difference between a motion vector of the current block andthe motion vector predictor of the current block; generating the motionvector predictor of the current block based on the decoded motion vectorpredictor information; and restoring the motion vector of the currentblock based on the motion vector predictor and the decoded difference,wherein the motion vector predictor is a motion vector predictorgenerated from one of a motion vector of an adjacent block referring toa first reference picture, if a block having a motion vector referringto the first reference picture identical to the first block exists fromamong adjacent blocks of the current block, and a motion vector of anadjacent block referring to a second reference picture other than thefirst reference picture, if the block having the motion vector referringto the first reference picture does not exist from among the adjacentblocks.

According to another aspect of the exemplary embodiments, there isprovided an apparatus for encoding a motion vector, the apparatuscomprising: a motion estimator that performs motion estimation on acurrent block of a current picture and generates a motion vector of acurrent block, the motion vector of the current block indicating aregion in a first reference picture that corresponds to the currentblock, based on the motion estimated current block; and a motion vectorencoder that determines whether an adjacent block having a motion vectorreferring to the first reference picture exists from among adjacentblocks encoded before the current block, one of generates a motionvector predictor using the motion vector of the adjacent block referringto the first reference picture, in response to determining that theadjacent block having the motion vector referring to the first referencepicture exists and generates the motion vector predictor by using amotion vector of an adjacent block referring to a second referencepicture other than the first reference picture, in response todetermining that the adjacent block having the motion vector referringto the first reference picture does not exist, and encodes a differencebetween the motion vector predictor and the motion vector of the currentblock as motion vector information of the current block.

According to another aspect of the exemplary embodiments, there isprovided an apparatus for decoding a motion vector, the apparatuscomprising: a motion vector decoder that decodes from a bitstream motionvector predictor information that indicates a motion vector predictor ofa current block of the bitstream, and decodes a difference between amotion vector of the current block and the motion vector predictor ofthe current block; and a motion compensator that generates the motionvector predictor of the current block based on the decoded motion vectorpredictor information, and restores the motion vector of the currentblock based on the motion vector predictor and the decoded difference,wherein the motion vector predictor is a motion vector predictorgenerated from one of a motion vector of an adjacent block referring toa first reference picture, if a block having a motion vector referringto the first reference picture identical to the first block exists fromamong adjacent blocks of the current block, and a motion vector of anadjacent block referring to a second reference picture other than thefirst reference picture, if the block having the motion vector referringto the first reference picture does not exist from among the adjacentblocks.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects will become more apparent by describing indetail exemplary embodiments thereof with reference to the attacheddrawings in which:

FIG. 1 is a block diagram of an apparatus for encoding a video,according to an exemplary embodiment;

FIG. 2 is a block diagram of an apparatus for decoding a video,according to an exemplary embodiment;

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 4 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 5 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 7 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 14 is a block diagram of an apparatus for encoding a motion vector,according to an exemplary embodiment;

FIGS. 15A and 15B are diagrams of motion vector predictor candidatesaccording to exemplary embodiments;

FIGS. 15C through 15E are diagrams of blocks having various sizes, whichare adjacent to a current block, according to exemplary embodiments;

FIG. 16 is a flowchart illustrating a method of encoding a motionvector, according to an exemplary embodiment;

FIG. 17 is a flowchart illustrating generating of a motion vectorpredictor, according to an exemplary embodiment;

FIGS. 18A through 18C are reference diagrams for describing determiningof a motion vector predictor, according to exemplary embodiments;

FIGS. 19A through 19C are reference diagrams for describing generationof motion vector predictor candidates, according to exemplaryembodiments;

FIG. 20 is a diagram for describing a method of generating a motionvector predictor in an implicit mode, according to an exemplaryembodiment;

FIG. 21 is a block diagram of an apparatus for decoding a motion vector,according to an exemplary embodiment; and

FIG. 22 is a flowchart illustrating a method of decoding a motionvector, according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the exemplary embodiments will be described more fully withreference to the accompanying drawings, in which the exemplaryembodiments are shown.

FIG. 1 is a block diagram of a video encoding apparatus 100, accordingto an exemplary embodiment.

The video encoding apparatus 100 includes a maximum coding unit splitter110, a coding unit determiner 120, and an output unit 130.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit for the current picture of an image. If thecurrent picture is larger than the maximum coding unit, image data ofthe current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an exemplary embodiment maybe a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc.,where a shape of the data unit is a square having a width and length insquares of 2, which is higher than 8. The image data may be output tothe coding unit determiner 120 according to the at least one maximumcoding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens, deeper encoding units according to depths may be splitfrom the maximum coding unit to a minimum coding unit. A depth of themaximum coding unit is an uppermost depth and a depth of the minimumcoding unit is a lowermost depth. Since a size of a coding unitcorresponding to each depth decreases as the depth of the maximum codingunit deepens, a coding unit corresponding to an upper depth may includea plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. The determined coded depth and the encoded imagedata according to the determined coded depth are output to the outputunit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to same depth inone maximum coding unit, it is determined whether to split each of thecoding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split to regions according to the depthsand the encoding errors may differ according to regions in the onemaximum coding unit, and thus the coded depths may differ according toregions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodimentinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splits from a maximum coding unit to a minimum codingunit. A first maximum depth according to an exemplary embodiment maydenote the total number of splits from the maximum coding unit to theminimum coding unit. A second maximum depth according to an exemplaryembodiment may denote the total number of depth levels from the maximumcoding unit to the minimum coding unit. For example, when a depth of themaximum coding unit is 0, a depth of a coding unit, in which the maximumcoding unit is split once, may be set to 1, and a depth of a codingunit, in which the maximum coding unit is split twice, may be set to 2.Here, if the minimum coding unit is a coding unit in which the maximumcoding unit is split four times, 5 depth levels of depths 0, 1, 2, 3 and4 exist, and thus the first maximum depth may be set to 4, and thesecond maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may select a size or shape of a dataunit for encoding the image data. In order to encode the image data,operations, such as prediction encoding, transformation, and entropyencoding, are performed, and at this time, the same data unit may beused for all operations or different data units may be used for eachoperation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit to perform the prediction encoding on the imagedata in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a predictionunit. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitiontype include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit.

In order to perform the transformation in the coding unit, thetransformation may be performed based on a data unit having a sizesmaller than or equal to the coding unit. For example, the data unit forthe transformation may include a data unit for an intra mode and a dataunit for an inter mode.

A data unit used as a base of the transformation will now be referred toas a transformation unit. Similarly to the coding unit, thetransformation unit in the coding unit may be recursively split intosmaller sized regions, so that the transformation unit may be determinedindependently in units of regions. Thus, residual data in the codingunit may be divided according to the transformation unit having the treestructure according to transformation depths.

A transformation depth indicating the number of splits to reach thetransformation unit by splitting the height and width of the coding unitmay also be set in the transformation unit. For example, in a currentcoding unit of 2N×2N, a transformation depth may be 0 when the size of atransformation unit is also 2N×2N, a transformation depth may be 1 whenthe size of the transformation unit is thus N×N, and a transformationdepth may be 2 when the size of the transformation unit is thus N/2×N/2.In other words, the transformation units having the tree structure maybe set according to the transformation depths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to exemplary embodiments,will be described in detail later with reference to FIGS. 3 through 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode. Also, information about a maximum size of the codingunit defined according to pictures, slices, or GOPs, and informationabout a maximum depth may be inserted into a header of a bitstream.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include maximum 4 of thecoding unit of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or large data amount is encodedin a conventional macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatus100, image compression efficiency may be increased since a coding unitis adjusted while considering characteristics of an image whileincreasing a maximum size of a coding unit while considering a size ofthe image.

FIG. 2 is a block diagram of a video decoding apparatus 200, accordingto an exemplary embodiment.

The video decoding apparatus 200 includes a receiver 210, an image dataand encoding information extractor 220, and an image data decoder 230.Various terms, such as a coding unit, a depth, a prediction unit, atransformation unit, and information about various encoding modes, forvarious operations of the video decoding apparatus 200 are similar tothose described with reference to FIG. 1 and the video encodingapparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, where thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and an inversetransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse transformationaccording to each transformation unit in the coding unit, based on theinformation about the size of the transformation unit of the coding unitaccording to coded depths, so as to perform the inverse transformationaccording to maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The video decoding apparatus 200 may obtain information about at leastone coding unit that generates the minimum encoding error when encodingis recursively performed for each maximum coding unit, and may use theinformation to decode the current picture. In other words, the codingunits having the tree structure determined to be the optimum codingunits in each maximum coding unit may be decoded.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 3 through 13.

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 3 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 4 is a block diagram of an image encoder 400 based on coding units,according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 performs inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determine partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 5 is a block diagram of an image decoder 500 based on coding units,according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units to consider characteristics of an image. Amaximum height, a maximum width, and a maximum depth of coding units maybe adaptively determined according to the characteristics of the image,or may be differently set by a user. Sizes of deeper coding unitsaccording to depths may be determined according to the predeterminedmaximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. Since a depthdeepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, a coding unit 640having a size of 8×8 and a depth of 3, and a coding unit 650 having asize of 4×4 and a depth of 4 exist. The coding unit 650 having the sizeof 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the coding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

The coding unit 650 having the size of 4×4 and the depth of 4 is theminimum coding unit and a coding unit of the lowermost depth. Aprediction unit of the coding unit 650 is only assigned to a partitionhaving a size of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 7 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 or the video decoding apparatus 200encodes or decodes an image according to coding units having sizessmaller than or equal to a maximum coding unit for each maximum codingunit. Sizes of transformation units for transformation during encodingmay be selected based on data units that are not larger than acorresponding coding unit.

For example, in the video encoding apparatus 100 or the video decodingapparatus 200, if a size of the coding unit 710 is 64×64, transformationmay be performed by using the transformation units 720 having a size of32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 9 only illustrates thepartition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d−1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By repeatedly performing the encoding, the video encoding apparatus100 may select a depth having the least encoding error by comparingencoding errors according to depths of the coding unit 900 to determinea coded depth, and set a corresponding partition type and a predictionmode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may individually perform intra prediction, motionestimation, motion compensation, transformation, and inversetransformation on a data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Information 0 Split (Encoding on Coding Unit having Sizeof 2N × 2N and Current Depth of d) Information 1 Prediction PartitionType Size of Transformation Unit Repeatedly Mode Encode IntraSymmetrical Asymmetrical Split Split Coding Units Inter PartitionPartition Information 0 of Information 1 of having Skip Type TypeTransformation Transformation Lower Depth (Only Unit Unit of d + 1 2N ×2N) 2N × 2N 2N × nU 2N × 2N N × N 2N × N 2N × nD (Symmetrical N × 2N nL× 2N Type) N × N nR × 2N N/2 × N/2 (Asymmetrical Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth. Thus, information about a partition type,prediction mode, and a size of a transformation unit may be defined forthe coded depth. If the current coding unit is further split accordingto the split information, encoding is independently performed on foursplit coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoding information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

When the partition type is set to be symmetrical, i.e. the partitiontype 1322, 1324, 1326, or 1328, a transformation unit 1342 having a sizeof 2N×2N is set if split information (TU size flag) of a transformationunit is 0, and a transformation unit 1344 having a size of N×N is set ifa TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

The motion estimation and compensation performed by the motion estimator420 and the motion compensator 425 of the video encoding apparatus 100of FIG. 4 and the motion compensator 560 of the video decoding apparatus200 of FIG. 5 will now be described in detail. Hereinafter, theprediction unit described above will be referred to as a block.

FIG. 14 is a block diagram of an apparatus 1400 for encoding a motionvector, according to an exemplary embodiment. The apparatus 1400includes elements related to encoding a motion vector, such as themotion estimator 420 and the entropy encoder 450 of FIG. 4, wherein theentropy encoder 450 may perform operations performed by a motion vectorencoder 1420 of FIG. 14.

Referring to FIG. 14, the apparatus 1400 according to the currentexemplary embodiment includes a motion estimator 1410 and the motionvector encoder 1420.

The motion estimator 1410 generates a motion vector of a current block,which indicates a region corresponding to the current block in a firstreference picture, by performing motion estimation on the current block.

Generally, a motion vector of a block is closely related to a motionvector of an adjacent block. Accordingly, a motion vector of a currentblock is estimated from a motion vector of an adjacent block, and onlythe motion vector of the adjacent block and a difference vector of thecurrent block are encoded to reduce an amount of bits to be encoded.Accordingly, the motion vector encoder 1420 generates a motion vectorpredictor by using motion vector information of adjacent blocks toencode motion vector information of a current block, and encodes only adifference between the motion vector predictor and the motion vector ofthe current block as the motion vector information of the current block.In detail, the motion vector encoder 1420 generates the motion vectorpredictor by using a motion vector of an adjacent block referring to thefirst reference picture when a block having a motion vector referring tothe first reference picture, which is referred to by the current block,exists from among adjacent blocks encoded before the current block, orby using a motion vector of a reference block referring to a referencepicture other than the first reference picture when the block having themotion vector referring to the first reference picture does not existfrom among the adjacent blocks, and then encodes the difference betweenthe generated motion vector predictor and the motion vector of thecurrent block as the motion vector information of the current block. Asdescribed above, a conventional image encoding apparatus uses a medianof motion vectors of adjacent blocks adjacent to left, top and upperright of the current block as a motion vector of the current block.However, the apparatus 1400 generates a motion vector predictorcandidate group from the adjacent blocks via one of various methods, anduses a motion vector predictor selected from the motion vector predictorcandidate group, aside from a median, to encode the motion vector of thecurrent block, thereby increasing image compression efficiency accordingto image characteristics.

The generating of the motion vector predictor performed by the motionvector encoder 1420 will now be described in detail.

FIGS. 15A and 15B are diagrams of motion vector predictor candidatesaccording to exemplary embodiments.

Referring to FIG. 15A, the motion vector encoder 1420 may use one of themotion vectors of the adjacent blocks encoded before the current blockas the motion vector predictor of the current block. Any one of motionvectors of a leftmost a0 block 1501, a uppermost left b0 block 1502,upper right c block 1503, upper left d block 1505, and a lower left eblock 1504 from among the adjacent blocks of the current block may beused as the motion vector predictor of the current block. Since videoencoding and decoding methods are performed based on coding units havingvarious sizes, which are classified according to depths, the motionvector of the lower left e block 1504 may also be used as the motionvector predictor of the current block. Referring back to FIG. 10, if thecurrent block is the coding unit 1020, the coding units 1014, 1016,1018, and 1022 at the top, upper left, upper right, left, and lower leftof the current block 1020 are encoded before the current block 1020. Inother words, since the coding unit 1018 is encoded before the codingunit 1020 including the current block, a motion vector of the blockadjacent to the lower left of a current block may also be used as amotion vector predictor of the current block considering that the codingunit 1018 is encoded in a coding unit having a deeper depth.

Referring to FIG. 15B, motion vectors of all adjacent blocks of thecurrent block may be used as the motion vector predictor of the currentblock. In other words, not only a motion vector of a leftmost a0 blockfrom among blocks 1510 adjacent to the top of the current block, butalso motion vectors of all blocks a0 through aN adjacent to the top ofthe current block may be used as the motion vector predictor of thecurrent block, and not only a motion vector of an uppermost b0 blockfrom among blocks 1520 adjacent to the left of the current block, butalso motion vectors of all blocks b0 through bN adjacent to the left ofthe current block may be used as the motion vector predictor of thecurrent block.

Alternatively, medians of motion vectors of adjacent blocks may be usedas the motion vector predictor. In other words, medians mv_a0, mv_b0,and mv_c may be used as the motion vector predictor of the currentblock. Here, the median mv_a0 is the motion vector of the a0 block, themedian mv_b0 is the motion vector of the b0 block, and the median mv_cis the motion vector of the c block.

However, motion vector predictor candidates may be limited according toa size of the current block and sizes of the adjacent blocks, which willbe described in detail with reference to FIGS. 15C through 15E.

FIGS. 15C through 15E are diagrams of blocks having various sizes, whichare adjacent to a current block, according to exemplary embodiments.

As described above, the image encoding and decoding methods encode anddecode an image by using coding units and prediction units havingvarious sizes, which are determined according to depths. Accordingly,sizes of the adjacent blocks of the current block may vary, and if thesize of the current block and the sizes of some adjacent blocks arelargely different, motion vectors of the some adjacent blocks may not beused as the motion vector predictor of the current block.

Referring to FIG. 15C, adjacent blocks 1014 through 1018 at the top of acurrent block 1010 have sizes smaller than the current block 1010. Sincea motion vector of the adjacent block 1012 having the same size as thecurrent block 1010 is highly likely to be identical or similar to amotion vector of the current block 1010, the motion vector encoder 1420may use only the motion vector of the adjacent block 1012 as the motionvector predictor.

Even if sizes are not the same, motion vectors of adjacent blocks havinga predetermined size or above may be used as the motion vectorpredictor. For example, the adjacent blocks 1012 and 1018 having ¼ orabove sizes compared to the current block 1010 may be used as the motionvector predictor.

Referring to FIG. 15D, a size of an adjacent block 1022 adjacent to theleft of a current block 1020 is 16 times as much as a size of thecurrent block 1020, and thus there is a remarkable size difference. Dueto the remarkable size difference, a motion vector of the adjacent block1022 is not likely to be identical or similar to a motion vector of thecurrent block 1020. Accordingly, the motion vector of the adjacent block1022 is not used as the motion vector predictor of the current block1020, and motion vectors of an adjacent block 1024 at the top of thecurrent block 1020 and an adjacent block 1026 at the upper right of thecurrent block 1020 may be used.

Referring to FIG. 15E, a size of a current block 1030 is larger thansizes of all adjacent blocks 1031 through 1037. Here, if motion vectorsof the adjacent blocks 1031 through 1037 are used as the motion vectorpredictor of the current block 1030, a number of motion vector predictorcandidates of the current block 1030 may be too much. As a differencebetween sizes of the current block 1030 and the adjacent blocks 1031through 1037 increases, the number of motion vector predictor candidatesalso increases. Accordingly, the motion vector encoder 1420 does not usemotion vectors of some adjacent blocks as the motion vector predictor ofthe current block.

For example, in FIG. 15E, the motion vectors of the adjacent block 1031adjacent to the lower left of the current block 1030 and the motionvector of the adjacent block 1037 adjacent to the upper right of thecurrent block 1030 may not be used as the motion vector predictor of thecurrent block 1030. In other words, if the size of the current block1030 is equal to or above a predetermined size, motion vectors ofadjacent blocks in a predetermined direction may not be used as themotion vector predictor of the current block 1030.

Alternatively, instead of generating the motion vector predictorcandidates by limiting the motion vector predictor candidates accordingto the size of the current block and the sizes of the adjacent blocks,the motion vector encoder 1420 may generate the motion vector predictorfrom the adjacent blocks based on whether a reference picture identicalto the first reference picture that is referred to by the current blockis used, whether a reference picture located in the same list directionas the first reference picture is used, and whether a reference picturelocated in a different list direction from the first reference pictureis used.

FIG. 16 is a flowchart illustrating a method of encoding a motionvector, according to an exemplary embodiment. While generating themotion vector predictor candidates, the motion vector encoder 1420 maygenerate the motion vector predictor candidates by using a motion vectorof an adjacent block using a reference picture identical to the firstreference picture that is referred to by the current block, a motionvector of an adjacent block using another reference picture located atthe same direction as the first reference picture if the referencepicture using the reference picture identical to the first referencepicture does not exist, and a motion vector of a motion block referringto another reference picture located in a different list direction asthe first reference picture if the adjacent block referring to the otherreference picture located in the same direction as the first referencepicture does not exist.

Referring to FIG. 16, the motion estimator 1410 generates the motionvector of the current block, which indicates the region corresponding tothe current block in the first reference picture, by performing motionestimation on the current block, in operation 1610.

If a block having a motion vector referring to the first referencepicture exists from among the adjacent blocks encoded before the currentblock, the motion vector encoder 1420 generates the motion vectorpredictor by using the motion vector of the adjacent block referring tothe first reference picture in operation 1620, and if the block havingthe motion vector referring to the first reference picture does notexist from among the adjacent blocks, the motion vector encoder 1420generates the motion vector predictor by using the motion vector of theadjacent block referring to the reference picture other than the firstreference picture in operation 1630.

In operation 1640, the motion vector encoder 1420 encodes a differencebetween the motion vector predictor and the motion vector of the currentblock as the motion vector information of the current block.

FIG. 17 is a flowchart illustrating in detail the generating of themotion vector predictor, according to an exemplary embodiment.

Referring to FIG. 17, the motion vector encoder 1420 extracts motioninformation of an adjacent block of a current block according to apredetermined scanning order, in operation 1710. The motion informationof the adjacent block includes reference picture information ref index_Nreferred to by the adjacent block and motion vector information of theadjacent block. The motion vector encoder 1420 selects a first motionvector predictor from a block adjacent to the left of the current block,a second motion vector predictor from a block adjacent to the top of thecurrent block, and a third motion vector predictor from a block locatedat the corner of the current block. In order to select the first throughthird motion vector predictors, a reference picture of each blocklocated at the top, left, and corner of the current block is comparedwith reference picture information referred to by the current block.Referring back to FIG. 15B, the predetermined scanning order is from topto bottom in the blocks 1520, i.e., from the block b0 to the block bn,and from the left to right in the blocks 1510, i.e., from the block a0to the block an. The c, e, and d blocks 1531, 1532, and 1533 may bescanned in an order of the block c 1531, the block d 1533, and the blocke 1532. However, the predetermined scanning order may differ.

In operation 1720, the motion vector encoder 1420 compares referencepicture information ref index_Cur referred to by the current block andthe reference picture information ref index_N of the adjacent block todetermine whether a reference picture of the adjacent block is identicalto a reference picture, i.e., the first reference picture, referred toby the current block. When it is determined that the reference pictureof the adjacent block is identical to the first reference picture inoperation 1720, the motion vector of the adjacent block is determined tobe the motion vector predictor in operation 1730. Operations 1720 and1730 are performed according to groups of the blocks 1510 located at thetop of the current block, the blocks 1520 located at the left of thecurrent block, and the blocks 1531 through 1533 located at the corner ofthe current block to generate the first through third motion vectorpredictors.

In operation 1740, it is determined whether operation 1720 is performedon all adjacent blocks according to the groups of blocks 1510, blocks1520, and blocks 1531 through 1533. If any one of the groups of blocks1510, blocks 1520, and blocks 1531 through 1533 does not include anadjacent block referring to the reference picture identical to the firstreference picture, it is determined whether an adjacent block referringto another reference picture that is not identical to the firstreference picture but located in a list direction of the current blockexists in operation 1750. Here, the list direction denotes an L0direction referring to a previous picture before the current picture andan L1 direction referring to a next picture after the current picture.

If it is determined that the adjacent block refers to the otherreference picture in operation 1750, a motion vector of the adjacentblock is determined to be the motion vector predictor in operation 1760.In operation 1770, it is determined whether operation 1750 is performedon all adjacent blocks, i.e., the blocks 1510, the blocks 1520, and theblocks 1531 through 1533. If any one of the groups of blocks 1510,blocks 1520, and blocks 1531 through 1533 does not include the adjacentblock referring to the other reference picture that is not identical tothe first reference picture but located in the list direction of thecurrent block, a motion vector of an adjacent block referring to anotherreference picture that is located in a different list direction from thefirst reference picture is determined to be the motion vector predictorof the current block in operation 1780.

In other words, the method and apparatus for encoding a motion vector,according to an exemplary embodiment, generate the first motion vectorpredictor from the adjacent blocks located at the left of the currentblock, the second motion vector predictor from the adjacent blockslocated at the top of the current block, and the third motion vectorpredictor from the adjacent blocks located at the corner of the currentblock, and at this time, the adjacent blocks are scanned in an order ofthe motion vector of the adjacent block referring to the first referencepicture, the motion vector of the adjacent block referring to the otherreference picture different from the first reference picture butexisting in the same list direction as the current block, and the motionvector of the adjacent block referring to the other reference picture inthe different list direction from the current block to determine themotion vector predictor candidates of the current block.

FIGS. 18A through 18C are reference diagrams for describing in detailthe determining of the motion vector predictor, according to exemplaryembodiments.

FIG. 18A is a diagram for describing generation of the motion vectorpredictor if an adjacent block referring to a first reference picture1810 referred to by the current block exists.

Referring to FIG. 18A, the motion vector encoder 1420 generates a firstmotion vector predictor from adjacent blocks 184 and 185 located at theleft of a current block 180, a second motion vector predictor fromadjacent blocks 181 through 183 located at the top of the current block180, and a third motion vector predictor from blocks (not shown) locatedat the corner of the current block 180. The generating of the secondmotion vector predictor from the blocks 181 through 183 will now bedescribed in detail as an example. The generating of the second motionvector predictor will be similarly applied while generating the firstand third motion vector predictors.

When the first reference picture 1810 is referred by the current block180 of a current picture 1800, the motion vector encoder 1420 scans theadjacent blocks 181 through 183 in an order from left to right todetermine whether a reference picture referred to by the adjacent blocks181 through 183 is identical to the first reference picture 1810. InFIG. 18A, It is assumed that the adjacent block 181 refers to a region1831 of a reference picture 1830 after the current picture 1800, theadjacent block 182 is a motion adjacent block predicted via a region1816 of the first reference picture 1810 identical to the current block180, and the block 183 is an intra predicted block. Here, the motionvector encoder 1420 determines a motion vector mv_182 of the adjacentblock 182 that is initially effective and referring to the firstreference picture 1810 as the second motion vector predictor. As such,when the adjacent block 182 refers to the first reference picture 1810identical to the current picture 1800, the motion vector mv_182 of theadjacent block 182 may not be separately scaled since a temporaldistance of the motion vector mv_182 is identical to that of a motionvector mv_cur of the current block 180 via region 1815. However, themotion vector encoder 1420 may not select the motion vector mv_182 ofthe adjacent block 182 as the second motion vector predictor if a sizeof the adjacent block 182 is below or equal to a predetermined thresholdvalue compared to the current block 180, as described above withreference to FIGS. 15C through 15E. If the adjacent block 182 referringto the first reference picture 1810 does not exist as shown in FIG. 18A,the generating of the motion vector predictor described with referenceto of FIG. 18B is performed.

FIG. 18B is a diagram for describing generation of the motion vectorpredictor when the adjacent block referring to the first referencepicture 1810 does not exist, but an adjacent block referring to anotherreference picture located in the same list direction as the firstreference picture 1810 exists.

Referring to FIG. 18B, it is assumed that the adjacent blocks 181 and182 refer to regions 1832, 1833 of the reference picture 1830 after thecurrent picture 1800, and the adjacent block 183 is a motion blockpredicted via a region 1821 of reference picture 1820, which is not thefirst reference picture 1810 but in the same list direction as the firstreference picture 1810, i.e., temporally before the current picture1800. Here, the motion vector encoder 1420 determines a motion vectormv_183 of the adjacent block 183 that is initially effective andreferring to the reference picture 1820 in the same list direction asthe first reference picture 1810, as the second motion vector predictor.As such, when the adjacent block 183 refers to the reference picture1820, since temporal distances of the first reference picture 1810 andthe reference picture 1820 are different from each other, the motionvector mv_183 of the adjacent block 183 is scaled while considering atemporal distance t1 between the current picture 1800 and the firstreference picture 1810, and a temporal distance t2 between the currentpicture 1800 and the reference picture 1820. In detail, the motionvector encoder 1420 performs scaling by multiplying the motion vectormv_183 by a value of (t1/t2), thereby determining mv_183×(t1/t2) as thesecond motion vector predictor. In other words, when CurrPOC denotes apicture order count (POC) of the current picture 1800, CurrRefPOCdenotes a POC of a reference picture referred to by the current block180, and NeighRefPOC denotes a POC of a reference picture referred to byan adjacent block, a scale value is calculated via an equation;Scale=(CurrPOC−CurrRefPOC)/(CurrPOC−NeighRefPOC), and the scaling isperformed by multiplying the determined motion vector by the scalevalue.

If even the adjacent block referring to the other reference picturelocated in the same list direction as the first reference picture 1810does not exist, the motion vector predictor may be generated, as will bedescribed with reference to FIG. 18C.

FIG. 18C is a diagram for describing the generating of the motion vectorpredictor when the adjacent block referring to the other referencepicture located in the same list direction as the first referencepicture 1810 does not exist.

Referring to FIG. 18C, it is assumed that the current block 180 refersto the first reference picture 1830 via region 1834 after the currentpicture 1800, the adjacent blocks 181 is an intra predicted block, theadjacent block 182 refers to the reference picture 1810 via region 1816before the current picture 1800, and the adjacent block 183 is a motionblock referring to the reference picture 1820 via region 1822 before thecurrent picture 1800. In other words, in FIG. 18C, an adjacent blockreferring to the first reference picture 1830 referred to by the currentblock 180 does not exist from among upper blocks of the current block180, and an adjacent block using a picture after the current picture1800 as a reference picture also does not exist. Here, the motion vectorencoder 1420 determines the motion vector mv_182 of the adjacent block182 that is initially effective and referring to the reference picture1810 in the different list direction from the first reference picture1830, i.e., before the current picture 1800, as the second motion vectorpredictor. When the adjacent block 182 refers to the reference picture1810 in the different list direction, instead of the first referencepicture 1830, since temporal distances of the first reference picture1830 and the reference picture 1810 are different from each other, themotion vector mv_182 of the adjacent block 182 is scaled whileconsidering a temporal distance t3 between the current picture 1800 andthe first reference picture 1830, a temporal distance t4 between thecurrent picture 1800 and the reference picture 1810, and the listdirection. In detail, the motion vector encoder 1420 performs scaling bymultiplying the motion vector mv_182 of the adjacent block 182 by avalue of −(t3/t4), and determines −(mv_182×(t3/t4)) as the second motionvector predictor.

The motion vector encoder 1420 determines the first and third motionvector predictors by performing the processes described with referenceto FIGS. 18A through 18C according to groups of blocks at the left andcorner of the current block 180. When the first through third motionvector predictors are determined, the motion vector encoder 1420 mayfurther include medians of the first through third motion vectorpredictors as the motion vector predictor candidates. If none of thefirst through third motion vector predictors exist, the motion vectorencoder 1420 sets a 0 vector as a median. If only one of the firstthrough third motion vector predictors exists, the motion vector encoder1420 sets an existing motion vector predictor as a median. If only twoof the first through third motion vector predictors exist, the motionvector encoder 1420 may set an non-existing motion vector predictor as a0 vector, and calculate a median according to components of x and yaxes, and include the calculated median in the motion vector predictorcandidates.

Meanwhile, while determining the medians of the motion vectors of theadjacent blocks, the motion vector encoder 1420 may calculate a medianby only using motion vectors in the same type. In other words, themotion vector encoder 1420 may determine the first through third motionvector predictors by only using motion vectors referring to the firstreference picture identical to the current block from among the motionvectors of the adjacent blocks of the current block, and include themedians of the first through third motion vector predicts in the motionvector predictor candidate of the current block.

Alternatively, as described above, the motion vector encoder 1420 maydetermine the first through third motion vector predictors by using themotion vector of the adjacent block referring to another referencepicture in the same list direction as the first reference picture, orthe motion vector of the adjacent block referring to another referencepicture in the different list direction from the first referencepicture, and include the medians of the third through third motionvector predictors in the motion vector predictor candidates of thecurrent block. Here, the motion vector encoder 1420 may include themedians of the first through third motion vector predictors in themotion vector predictor candidates only when all of the first throughthird motion vector predictors determined in the adjacent blocks referto the other reference picture different from the current block.

FIGS. 19A through 19C are reference diagrams for describing generationof the motion vector predictor candidates, according to exemplaryembodiments.

FIG. 19A is a diagram for describing a method of calculating a motionvector predictor of a bi-directional predictive picture (B picture),according to an exemplary embodiment. In the B picture, where a currentpicture 1910 including a current block 1900 performs bi-directionalprediction, a motion vector generated based on a temporal distance maybe a motion vector predictor candidate.

A motion vector predictor mv_temporal of the current block 1900 of thecurrent picture 1910 may be generated by using a motion vector of aco-located block 1920 of a temporally previous picture 1912. Forexample, when a motion vector mv_colA of the co-located block 1920 isgenerated with respect to a block 1922 of a temporally following picture1914 of the current picture 1910, a temporal distance t5 between thecurrent picture 1900 and picture 19140, and a temporal distance t6between pictures 1912 and 1914, motion vector predictor candidatesmv_L0A and mv_L1A of the current block 1900 may be generated as follows:mv_L1A=(t5/t6)×mv_colAmv_L0A=mv_L1A−mv_colA

Here, mv_L0A denotes a motion vector predictor of the current block 1900with respect to the temporally previous picture 1912, and mv_L1A denotesa motion vector predictor of the current block 1900 with respect to thetemporally following picture 1914.

In FIG. 19A, the current picture 1910 constituting the B picture existsbetween the temporally previous picture 1912 and the temporallyfollowing picture 1914. Here, when the motion vector mv_colA of theco-located block 1920 is generated with respect to the temporallyfollowing picture 1914, the motion vector of the current block 1900 maybe more accurately predicted based on the motion vector predictormv_L1A. In other words, the motion vector of the current block 1900 maybe more accurately predicted when the motion vector mv_colA is in adirection shown in FIG. 19A than when the motion vector mv_colA is in anopposite direction from the direction shown in FIG. 19A, i.e., when themotion vector mv_colA is generated with respect to another picturebefore the temporally previous picture 1912.

Accordingly, when a direction from the current block 1900 to theco-located block 1920 is a List0 direction, the motion vector mv_colA ofthe co-located block 1920 should be in a List1 direction so that thecurrent picture 1910 exists between the temporally previous picture 1912and the temporally following picture 1914 as shown in FIG. 19A, therebyaccurately predicting the motion vector of the current block 1900 basedon the motion vector mv_colA.

Also, since the current picture 1910, the temporally previous picture1912, and the temporally following picture 1914 of FIG. 19A are arrangedin a time order, the motion vector predictor mv_temporal of the currentblock 1900 may be generated based on a POC. Since a picture referred toby the current block 1900 may not be one of the current picture 1910,the temporally previous picture 1912, and the temporally followingpicture 1914, the motion vector predictor mv_temporal of the currentblock 1900 is generated based on the POC.

For example, when CurrPOC denotes a POC of a current picture andCurrRefPOC denotes a POC of a picture referred to by the currentpicture, a motion vector predictor of a current block may be generatedas follows:Scale=(CurrPOC−CurrRefPOC)/(ColPOC−ColRefPOC)mv_temporal=Scale*mv_colA

Here, ColPOC denotes a POC of the temporally previous picture 1912included in the co-located block 1920, and ColRefPOC denotes a POC ofthe temporally following picture including the block 1922 referred to bythe co-located block 1920.

FIG. 19B is a diagram for describing a method of generating a motionvector predictor of a B picture, according to another exemplaryembodiment. Comparing the method of FIG. 19A and the method of FIG. 19B,the temporally following picture 1914 includes a block 1930 in the samelocation as the current block 1900 of the current picture 1910.

Referring to FIG. 19B, the motion vector predictor of the current block1900 of the current picture 1910 may be generated by using a motionvector of a co-located block 1930 of the temporally following picture1914. For example, when a motion vector mv_colB of the co-located block1930 is generated with respect to a block 1932 of the temporallyprevious picture 1912, a temporal distance t7 between the currentpicture 1910 and the picture 1912, and a temporal distance t8 betweenthe pictures 1912 and 1914, motion vector predictor candidates mv_L0Band mv_L1B of the current block 1900 may be generated as follows:mv_L0B=(t7/t8)×mv_colBmv_L1B=mv_L0B−mv_colB

Here, mv_L0B denotes the motion vector predictor of the current picture1910 with respect to the temporally previous picture 1912, and mv_L1Bdenotes the motion vector predictor of the current block 1900 withrespect to the temporally following picture 1914.

Like FIG. 19A, the current picture 1910 constituting the B pictureexists between the temporally previous picture 1912 and the temporallyfollowing picture 1914 in FIG. 19B. Accordingly, when the motion vectormv_colB of the co-located block 1930 is generated with respect to thetemporally previous picture 1912, the motion vector of the current block1900 may be more accurately predicted based on the motion vector mv_L0B.In other words, the motion vector of the current block 1900 may be moreaccurately predicted when the motion vector mv_colB is in a directionshown in FIG. 19B than when the motion vector mv_colB is in an oppositedirection from the direction shown in FIG. 19B, i.e., when the motionvector mv_colB is generated with respect to another picture after thetemporally following picture 1914.

Accordingly, when a direction from the current block 1900 to theco-located block 1930 is a List1 direction, the motion vector mv_colB ofthe co-located block 1930 should be in a List0 direction so that thecurrent picture 1910 exists between the temporally previous picture 1912and the temporally following picture 1914 as shown in FIG. 19B, therebyaccurately predicting the motion vector of the current block 1900 basedon the motion vector mv_colB.

Also, since a picture referred to by the current block 1900 may not beone of the temporally previous picture 1912 and the temporally followingpicture 1914, the motion vector predictor of the current block 1900 isgenerated based on the POC. For example, when CurrPOC denotes a POC of acurrent picture and CurrRefPOC denotes a POC of a picture referred to bythe current picture, a motion vector predictor of a current block may begenerated as follows:Scale=(CurrPOC−CurrRefPOC)/(ColPOC−ColRefPOC)mv_temporal=Scale*mv_colB

Here, ColPOC denotes a POC of the temporally following picture 1914including the co-located block 1930, and ColRefPOC denotes a POC of thetemporally previous picture 1912 including the block 1932 referred to bythe co-located block 1930.

The motion vector encoder 1420 may use any one of the methods of FIGS.19A and 19B while generating the motion vector predictor of the currentblock 1900 of the B picture. In other words, since the motion vectorencoder 1420 generates the motion vector predictor by using the motionvector and the temporal distance of the co-located block 1920 or 1930,the motion vector predictor is generated by using one of the methods ofFIGS. 19A and 19B only when the motion vector of the co-located block1920 or 1930 exists. Accordingly, the motion vector encoder 1420generates the motion vector predictor of the current block 1900 by onlyusing a block having a motion vector from among the co-located blocks1920 and 1930.

For example, when the co-located block 1920 of the temporally previouspicture 1912 is encoded by using intra prediction, instead of interprediction, the motion vector of the co-located block 1920 does notexist, and thus the motion vector predictor of the current block 1900cannot be generated by using the method of FIG. 19A.

When the motion vector encoder 1420 generates the motion vectorpredictor of the current block 1900 of the B picture as shown in FIGS.19A and 19B, both of the co-located block 1920 of the temporallyprevious picture 1912 and the co-located block 1930 of the temporallyfollowing picture 1914 may be used. Accordingly, a decoder for decodinga motion vector must determine which block is used to generate themotion vector predictor from among the co-located blocks 1920 and 1930,to decode the motion vector predictor.

Accordingly, the motion vector encoder 1420 may encode information forspecifying which block is used, and insert the encoded information intoa block header or a slice header.

FIG. 19C is a diagram for describing a method of generating a motionvector predictor of a predictive picture (P picture), according to anexemplary embodiment.

Referring to FIG. 19C, the motion vector predictor of the current block1900 of the current picture 1910 may be generated by using a motionvector of a co-located block 1940 of the temporally previous picture1912. For example, when a motion vector mv_colC of the co-located block1940 is generated with respect to a block 1942 of another temporallyprevious picture 1916, a temporal distance t9 between the pictures 1912and 1916, and a temporal distance t10 between the pictures 1910 and1916, a motion vector predictor mv_L0C of the current block 1900 may begenerated as follows:mv_L0C=(t10/t9)×mv_colC

The motion vector mv_L0C may be generated based on a POC as describedabove with reference to FIGS. 19A and 19B. The motion vector mv_L0C maybe generated based on a POC of the current picture 1910, a POC of apicture referred to by the current picture 1910, a POC of the temporallyprevious picture 1912, or a POC of the other temporally previous picture1916.

Since the current picture 1910 is a P picture, only one motion vectorpredictor candidate of the current block 1900 is generated in FIG. 19C,unlike FIGS. 19A and 19B.

In summary, a group C of motion vector predictor candidates generated bythe motion vector encoder 1420 may be as follows.

C={median(mv_a′, mv_b′, mv_c′), mv_a′, mv_b′, mv_c′, mv_temporal}

Here, as described above with reference to FIGS. 16 through 18, mv_a′denotes a first motion vector predictor constituting a motion vector ofan adjacent block initially effective from a left block of a currentblock, mv_b′ denotes a second motion vector predictor constituting amotion vector of an adjacent block initially effective from an upperblock of the current block, and mv_c′ denotes a third motion vectorpredictor constituting a motion vector of an adjacent block effectivefrom blocks located at corners of the current block. Here, regardingeffectiveness of an adjacent block, i) whether an adjacent block refersto a first reference picture referred to by a current block, ii) whetheran adjacent block refers to a reference picture other than the firstreference picture, which exists in the same list direction as the firstreference picture, and iii) whether an adjacent block refers to areference picture existing in a different list direction from the firstreference picture are sequentially determined, and a motion vector of aninitially scanned adjacent block that satisfies the above condition isdetermined as a motion vector predictor candidate. Also, median( )denotes a median and mv_temporal denotes motion vector predictorcandidates generated by using the temporal distance described above withreference to FIGS. 19A through 19C. As described above, the motionvector encoder 1420 may calculate a median by only using motion vectorsin the same type while determining medians of motion vectors of adjacentblocks as motion vector predictor candidates. In other words, the motionvector encoder 1420 may determine the first through third motion vectorpredictors by only using motion vectors referring to the first referencepicture from among the motion vectors of the adjacent blocks of thecurrent block, and include medians of the first through third motionvector predictors in the motion vector predictor candidates of thecurrent block. Alternatively, as described above, the motion vectorencoder 1420 may determine the first through third motion vectorpredictors by using the motion vector of the adjacent block referring tothe reference picture in the same list direction as the first referencepicture or the motion vector of the adjacent block referring to thereference picture in the different list direction from the firstreference picture, and include the medians of the first through thirdmotion vector predictors in the motion vector predictor candidates ofthe current block. Here, the motion vector encoder 1420 may include themedians of the first through third motion vector predictors in themotion vector predictor candidates only when all of the first throughthird motion vector predictors refer to the reference picture other thanthe first reference picture.

The motion vector encoder 1420 may add information about which motionvector predictor from among elements of the group C of motion vectorpredictor candidates is used to a bitstream, as information about amotion vector predictor. In detail, in order to specify one element inthe group C, the motion vector encoder 1420 may assign an index to eachmotion vector predictor candidate, and add index information of a motionvector predictor actually used to encode a motion vector to a bitstream.

Also, when the group C is generated, the motion vector encoder 1420 mayprioritize useable motion vector predictors to use the usable motionvector predictors according to priority while encoding the motionvector. For example, the motion vector encoder 1420 prioritizesmedian(mv_a′, mv_b′, mv_c′), mv_a′, mv_b′, mv_c′, and mv_temporal in thestated order to determine a motion vector predictor to be used to encodethe motion vector.

The skilled artisan will understand that motion vector predictorcandidates other than the above-described motion vector predictorcandidates may be used.

Alternatively, the motion vector encoder 1420 may classify the adjacentblocks into the N (N is integer) adjacent groups and determine N motionvector predictors for respective N adjacent groups by using the motionvector of the adjacent block referring to another reference picture inthe same list direction as the first reference picture, or the motionvector of the adjacent block referring to another reference picture inthe different list direction from the first reference picture, andinclude the medians of the third through third motion vector predictorsin the motion vector predictor candidates of the current block. Forexample, referring back to FIG. 15B, the motion vector encoder 1420 maygroup the adjacent blocks into two groups. Here, one group includes a0through a_(n) block 1510 adjacent to the top of the current block andupper right c block 1531. Another group includes b0 through b_(n) block1520 adjacent to the left of the current block and a lower left e block1532. After grouping the adjacent blocks of the current block into twogroups, the motion vector encoder 1420 determine two motion vectorpredictors for respective two groups, as described above. Also, themotion vector encoder 1420 may classify the adjacent blocks into the Nadjacent groups according to the location of the adjacent blocks anddetermine N motion vector predictors for respective N adjacent groups.

Meanwhile, the motion vector encoder 1420 may only encode informationindicating that the motion vector predictor of the current block isencoded based on a block or pixel included in an adjacent region encodedbefore the current block. In other words, the motion vector encoder 1420may not encode the information for specifying the motion vectorpredictor, and may encode only the information indicating that themotion vector predictor is generated. Generally, in Codec, such asMPEG-4 H.264 or MPEG-4 AVC, motion vectors of adjacent blocks encodedbefore a current block are used to predict a motion vector of thecurrent block. When medians of motion vectors of previously encodedadjacent blocks located at the left, top, and upper right of the currentblock are determined to be used as the motion vector predictors of thecurrent block, information for selecting one of the motion vectorpredictor candidates may not be separately encoded.

In other words, when information indicating that the motion vectorpredictor of the current block is encoded in an implicit mode is encodedduring an encoding process, the medians of the motion vectors of theadjacent blocks at the left, top, and upper right of the current blockmay be used as the motion vector predictors of the current block duringa decoding process. Specifically, a method and apparatus for encoding amotion vector, according to another exemplary embodiment, may generate amotion vector predictor by using adjacent pixel values encoded before acurrent block as templates. This will be described in detail withreference to FIG. 20.

FIG. 20 is a diagram for describing a method of generating a motionvector predictor in an implicit mode, according to an exemplaryembodiment.

Referring to FIG. 20, a motion vector predictor of a current block 2000of a current picture 2010 is generated by using pixels 2022 included inan adjacent region 2020 encoded before the current block 2000. Pixels2024 corresponding to the pixels 2022 are determined by searching areference picture 2012 by using the pixels 2022. The pixels 2024 may bedetermined by calculating a cost, such as a sum of absolute difference(SAD). When the pixels 2024 are determined, motion vectors mv_templateof the pixels 2022 are determined, and the motion vectors mv_templatemay be used as motion vector predictors of the current block 2000. Whenthe motion vectors mv_template are searched for in the reference picture2012, the group C of the motion vector predictor candidates describedabove may be used.

FIG. 21 is a block diagram of an apparatus 2100 for decoding a motionvector, according to an exemplary embodiment.

The apparatus 2100 of FIG. 21 includes elements related to encoding of amotion vector, such as the motion compensator 560 and the entropydecoder 520 of FIG. 5, wherein the entropy decoder 520 of FIG. 5 mayperform operations performed by a motion vector decoder 2110 of FIG. 21.

Referring to FIG. 21, the apparatus 2100 includes the motion vectordecoder 2110 and a motion compensator 2120.

The motion vector decoder 2110 decodes information about a motion vectorpredictor of a current block that is decoded from a bistream, and adifference between a motion vector of the current block and the motionvector predictor of the current block. In detail, the motion vectordecoder 2110 decodes index information indicating a motion vectorpredictor from among motion vector predictor candidates described above,which is used as a motion vector predictor of the current block to bedecoded. If the motion vector predictor candidates include mv_temporaldescribed above with reference to FIGS. 19A through 19C, informationabout whether a co-located block used to generate mv_temporal is a blockof a temporally previous picture or a temporally following picture ofthe current picture is also decoded. If a motion vector predictor of acurrent block is encoded in an implicit mode as shown in FIG. 20, modeinformation indicating the implicit mode is decoded.

The motion compensator 2120 generates the motion vector predictor of thecurrent block based on the information about the motion vector predictorof the current block. In other words, the motion compensator 2120determines which motion vector predictor is used as the motion vectorpredictor of the current block from the information about the motionvector predictor, and restores a motion vector of the current block byadding the determined motion vector predictor and a decoded difference.In the motion vector predictor encoded as described above with referenceto FIGS. 16 through 18, when a block having a motion vector referring tothe first reference picture like the current block does not exist fromamong adjacent blocks, the motion vector predictor may be determined byusing a motion vector of an adjacent block referring to a referencepicture other than the first reference picture.

FIG. 22 is a flowchart illustrating a method of decoding a motionvector, according to an exemplary embodiment.

Referring to FIG. 22, the motion vector decoder 2110 decodes informationabout a motion vector predictor of a current block decoded from abitstream, and decodes a difference between a motion vector of thecurrent block and the motion vector predictor of the current blockrespectively in operations 2210 and 2220. As described above, the motionvector decoder 2110 decodes index information indicating a motion vectorpredictor from among motion vector predictor candidates, which is usedas a motion vector predictor of the current block to be decoded. If themotion vector predictor candidates include mv_temporal described abovewith reference to FIGS. 19A through 19C, information about whether aco-located block used to generate mv_temporal is a block of a temporallyprevious picture or a temporally following picture of the currentpicture is also decoded. If a motion vector predictor of a current blockis encoded in an implicit mode as shown in FIG. 20, mode informationindicating the implicit mode is decoded.

The motion compensator 2120 generates the motion vector predictor of thecurrent block based on the information about the motion vector predictorin operation 2230, and restores the motion vector of the current blockby adding the motion vector predictor and the difference. As describedabove, in the motion vector predictor encoded as described above withreference to FIGS. 16 through 18, when a block having a motion vectorreferring to the first reference picture like the current block does notexist from among adjacent blocks, the motion vector predictor may bedetermined by using a motion vector of an adjacent block referring to areference picture other than the first reference picture.

The exemplary embodiments can also be embodied as computer readablecodes on a computer readable recording medium. The computer readablerecording medium is any data storage device that can store data whichcan be thereafter read by a computer system. Examples of the computerreadable recording medium include read-only memory (ROM), random-accessmemory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical datastorage devices, etc. The computer readable recording medium can also bedistributed over network coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion.Alternatively, the exemplary embodiments may be embodied ascomputer-readable transmission media, such as carrier waves, fortransmission over a network, such as the Internet.

The apparatuses, encoders, and decoders of the exemplary embodiments mayinclude a bus coupled to every unit of the apparatus, at least oneprocessor (e.g., central processing unit, microprocessor, etc.) that isconnected to the bus for controlling the operations of the apparatusesto implement the above-described functions and executing commands, and amemory connected to the bus to store the commands, received messages,and generated messages.

While aspects of the application have been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims. The exemplaryembodiments should be considered in descriptive sense only and not forpurposes of limitation. Therefore, the scope of the invention is definednot by the detailed description, but by the appended claims, and alldifferences within the scope will be construed as being included in thepresent invention.

What is claimed is:
 1. A method of decoding an image, the methodcomprising: obtaining a prediction mode of a current block from abitstream; when the prediction mode of the current block isinter-prediction, obtaining motion vector predictor candidates of thecurrent block using at least one motion vector of neighboring blocksadjacent to the current block; obtaining a motion vector predictor ofthe current block from among the motion vector predictor candidatesbased on motion vector predictor information obtained from thebitstream; and restoring a motion vector of the current block based onthe motion vector predictor and a difference motion vector, wherein theat least one motion vector of neighboring blocks is obtained bysearching for an available motion vector from the neighboring blocksadjacent to a left side of the current block according to a first scanorder, and by searching for an available motion vector from theneighboring blocks adjacent to an upper side of the current blockaccording to a second scan order, wherein the neighboring blocksadjacent to the left side of the current block comprise a lower leftblock and an upper block located to the upper side of the lower leftblock, wherein the first scan order indicates a scan order which scansthe neighboring blocks adjacent to the left side of the current blockfrom the lower left block to the upper block, and wherein the secondscan order indicates a scan order which scans the neighboring blocksadjacent to the upper left side of the current block from right side toleft side.
 2. The method of claim 1, wherein the first motion vectorpredictor and the second motion vector predictor are motion vectors ofmotion blocks identified firstly from among motion vectors of theneighboring blocks according to the first order and the second order,respectively.
 3. An apparatus that encodes an image, the apparatuscomprising: a motion estimator that performs motion estimation on acurrent block of a current picture and obtains a motion vector of acurrent block, the motion vector of the current block indicating aregion in a reference picture that corresponds to the current block,based on the motion estimation; and a motion vector encoder thatgenerates motion vector predictor candidates of the current block usingat least one motion vector of neighboring blocks adjacent to the currentblock, obtains a motion vector predictor of the current block from amongthe motion vector predictor candidates, and encodes a difference betweenthe motion vector predictor and the motion vector of the current blockas motion vector information of the current block, wherein the at leastone motion vector of neighboring blocks is obtained by searching for anavailable motion vector from the neighboring blocks adjacent to a leftside of the current block according to a first scan order, and bysearching for an available motion vector from the neighboring blocksadjacent to an upper side of the current block according to a secondscan order, wherein the neighboring blocks adjacent to the left side ofthe current block comprise a lower left block and an upper block locatedto the upper side of the lower left block, wherein the first scan orderindicates a scan order which scans the neighboring blocks adjacent tothe left side of the current block from the lower left block to theupper block, and wherein the second scan order indicates a scan orderwhich scans the neighboring blocks adjacent to the upper side of thecurrent block from right side to left side.